The present invention relates to a wheel bearing apparatus which is comprised of a rotating inside member provided with a detected member, an outside member, and a wheel rotation speed detector having a detection end portion which includes a sensor in opposition to the detected member, and a circuit housing which is connected to the detection end portion and which includes a circuit to process the detection signal received from the sensor, being able to be used, for example, on an automotive drive wheel of the type provided with an antilock brake system which detects the wheel velocity by means of a rotation speed detector and controls the wheels based on this detected speed so that they do not lock when the brakes are suddenly applied.
A wheel rotational speed detector mounted on a wheel bearing of type which constitutes an essential component in an antilock brake system as described above requires high detection precision and extremely high vibration resistance and sealing performance in order to maintain high detection precision. If these requirements are not provided, the detector may be damaged by vibrations and penetrated by water or other foreign matter, thus causing the rotational speed detector to break down or malfunction, or to lead even to a major accident.
At the same time, small, compact rotational speed detectors installed on wheel bearing apparatuses are desirable in order to minimize the restrictions of the installation space and to make the wheel bearing apparatus itself more compact. However, at the current level of technology, the rotational speed detector is unavoidably large because of the need for high vibration resistance and sealing performance as described above, and it is not possible to completely embed the rotational speed detector in the outside member.
Conventionally, an axle bearing apparatus provided with a rotational speed detector as thus described comprises, as shown in FIG. 18, an inside member 104 having a basically cylindrically shaped main member 101 and a flange 102 at the end portion 101a of main member 101, the flange 102 projecting to the outside and being used for mounting to a wheel. A wheel axle (not shown in the figure) passes through through-hole 104a at the center of main member 101. The inside member 104 is provided with a detected member 103 which is comprised of multiple projections 103a at regular intervals around the circumference of main member 101 and projecting to the outside in the radial direction. This wheel bearing apparatus is also provided with an outside member 106 on the same axis as the inside member 104 and fixed to a chassis (not shown in the figure) at mounting portion 105, multiple rolling elements 107 provided between raceway surfaces 104a, 104b of inside member 104 and raceway surfaces 106a, 106b of outside member 106 so as to roll in the circumferential direction on the raceways, and a cylindrically shaped rotational speed detector 112 mounted in outside member 106 and comprised of a detector end portion 110 and a circuit housing 111. Said detector member 110 is mounted in opposition to detected member 103 of inside member 104 and includes a sensor which is not shown in the figure, and circuit housing 111 houses a circuit, not shown in the figure, which processes the detection signal received from the sensor. The rotational speed of the inside member 104 is detected by the rotational speed detector 112. (See U.S. Pat. No. 4,778,286.)
However, in a conventional wheel bearing apparatus provided with a wheel rotational speed detector as described above, said rotational speed detector 112 has a simple cylindrical shape extending in the axial direction and cannot be made to be a sufficiently compact device with the current state of technology, the problem is that when the rotational speed detector 112 is mounted on outside member 106 so that the detector end portion 110 is in opposition to the detected member 103 of the inside member 104, circuit housing 111 projects significantly to the outside in the radial direction from the outside surface of the outside member of the main body. While the rotational speed detector 112 shown in FIG. 18 is small, the detector is actually quite large when the signal processing circuit is housed inside and the rotational speed detector 112 actually extends beyond the outside edge of mounting member 105 in common applications. Thus, because the rotational speed detector 112 projects significantly, the wheel bearing apparatus cannot be handled easily during transportation or installation of the wheel bearing apparatus because the protruding rotational speed detector 112 can easily strike other parts and be subjected to unanticipated external forces which could result in damage to the rotational speed detector.